Among the various video display systems available in the art, an optical projection system is known to be capable of providing a high quality display in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors, wherein each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of, e.g., an optical baffle. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIGS. 1 and 2, there are shown a cross sectional and a perspective views, respectively, of an array 10 of M.times.N thin film actuated mirrors 11 for use in an optical projection system, disclosed in a copending commonly owned application, U.S. Ser. No. 08/340,762, entitled "ARRAY OF THIN FILM ACTUATED MIRRORS FOR USE IN AN OPTICAL PROJECTION SYSTEM AND METHOD FOR THE MANUFACTURE THEREOF", comprising an active matrix 12, an array 13 of M.times.N thin film actuating structures 14, an array 15 of M.times.N supporting members 16 and an array 17 of M.times.N mirror layers 18.
The active matrix 12 includes a substrate 19, an array of M.times.N transistors(not shown) and an array 20 of M.times.N connecting terminals 21. Each of the actuating structures 14 in the array 10 is provided with a first and a second actuating parts 22(a), 22(b) and a center part 22(c) therebetween, the first and second actuating parts 22(a), 22(b) being identically structured, wherein each of the first and second actuating parts 22(a), 22(b) has at least a thin film layer 23 of an electrodisplacive material, e.g., piezoelectric material, including a top and a bottom surfaces 24, 25, an elastic layer 26 having a bottom surface 41, and a first and a second electrodes 28, 29. The elastic layer 26 is placed on the top surface 24 of the electrodisplacive thin film layer 23. The first and second electrodes 28, 29 are located on the top and bottom surfaces 24, 25 of the electrodisplacive thin film layer 23, respectively, wherein an electrical signal applied across the electrodisplacive thin film layer 23 located between the first and second electrodes 28, 29 causes a deformation thereof, and hence the actuating parts 22(a), 22(b). Each of the supporting members 16 is used for holding each of the actuating structures 13 in place and also for electrically connecting each of the actuating structures 14 with the active matrix 12. Each of the mirror layers 18 includes a first side 30, a second opposing side 31, and a center portion 32 therebetween as shown in FIG. 2, wherein the first side 30, the second opposing side 31 and the center portion 32 of each of the mirror layers 18 are secured on top of the first, second actuating and center parts 22(a), 22(b), 22(c) of each of the actuating structures 14, respectively, such that when the first and second actuating parts 22(a), 22(b) in each of the actuating structures 14 deform in response to the electrical signal, the center part 22(c) in each of the actuating structures 13, and hence the center portion 32 of the corresponding mirror layer 18, tilts while remaining planar, thereby allowing all of the center portion 32 to reflect the light beams, resulting in an increased optical efficiency.
One of the major shortcomings of the above described array 10 of thin film actuated mirrors 11 is that it incorporates therein the active matrix 12 including the array of transistors for providing driving and image signals to each of the thin film actuated mirrors 11 to thereby elevate the cost of manufacturing the array 10 too high.